It’s probably because we don’t really know why the Kangaroo is fighting the koala, why it’s funny that the koala died, and what the relation the koala had to the kangaroo besides natuarl location. Also the highest ranking disease killing koala is Chlamydia.

Hah well, you just pointed out every element of this comic that I still find hilarious. Of course they don’t have anything else in common except location, and a dying koala is inherently funny either way… I think.